The invention discloses an ultrahigh frequency sensor for cable partial discharge online monitoring, and belongs to the technical field of cable terminal discharge monitoring. The ultrahigh frequency sensor for the cable partial discharge online monitoring solves the problem that an existing ultra wide band frequency-independent antenna can not have the characteristics of being low in transmission loss and ensuring a low frequency end at the same time. The ultrahigh frequency sensor for the cable partial discharge online monitoring comprises an antenna substrate, an equiangular helical antenna section, an Archimedes antenna section, a micro-strip line substrate, central conduction band micro-strip lines and earth plate micro-strip lines, wherein the equiangular helical antenna section and the Archimedes antenna section are spirally arranged on the antenna substrate from the center to the direction of an outer ring in sequence, two tail ends of the equiangular helical antenna section are correspondingly connected with two head ends of the Archimedes antenna section in a one-to-one mode, a protruding rectangular connecting column is arranged in the center of a head end side of the micro-strip line substrate, the central conduction band micro-strip lines cover the center of the obverse side of the micro-strip line substrate from the head end to the tail end, and the earth plate micro-strip lines cover the center of the reverse side of the micro-strip line substrate from the head end to the tail end. The ultrahigh frequency sensor for the cable partial discharge online monitoring is used for online monitoring of ultrahigh frequency signals of cable partial discharge.